MICROBIAL NECROMASS WITHIN AGGREGATES STABILIZES PHYSICALLY-PROTECTED C RESPONSE TO CROPLAND MANAGEMENT

The interactions of soil microorganisms and structure regulate the degradation and stabilization processes of soil organic carbon(SOC). Microbial necromass is a persistent component of SOC, and its magnitude of accumulation dependent on management and aggregate sizes. A meta-analysis of 121 paired measurements was conducted to evaluate the management effects on contributions of microbial necromass to SOC depending on aggregate fractions. Results showed that the contribution of fungal necromass to SOC increased with aggregate sizes, while bacterial necromass had a higher proportion in silt and clay. Cropland management increased total and fungal necromass in large macroaggregates(47.1% and 45.6%), small macroaggregates(44.0% and 44.2%), and microaggregates(38.9% and 37.6%).Cropland management increased bacterial necromass independent of aggregate fraction sizes. Greater fungal necromass was increased in macroaggregates in response to manure(26.6% to 28.5%) and no or reduced tillage(68.0% to 73.5%). Cover crops increased bacterial necromass by 25.1%in small macroaggregates. Stimulation of microbial necromass was proportional to the increases of SOC within soil aggregates, and the correlation was higher in macroaggregates. Increasing microbial necromass accumulation in macroaggregates can, therefore, be considered as a central component of management strategies that aim to accelerate C sequestration in agricultural soils.